The main thing I see wrong here is that the basking lights need to be on one end of the cage or the other, not right in the middle. And if your planning to elevate the basking platform anyway, either cap the hole for the mortar tub and set it up there or maybe use the other end and stack something up starting from the cage floor, like cinder blocks or bricks or whatever. That way the lizard won't undermine the basking platform while digging. The advantage to the mortar tub water area would be the option of installing a drain to make cleaning easier.